A number of MOSFET gate-drive schemes utilize an active switch between gate and source to provide fast turn-off of the MOSFET. In these circuit arrangements, the gate is ordinarily clamped at zero volts with respect to the source, sometimes providing only 1.5 volts of margin against noise-induced MOSFET turn-on, depending on the actual threshold voltage of the device.
Noise susceptibility in high power MOSFET gate drive circuits becomes increasingly troublesome as switching speed and power level increase. High current switching paths and parasitic couplings superimpose spurious spikes into the gate drive circuits. Under certain conditions of polarity and amplitude, noise voltage pulses in the gate-drive circuit may be such that their effects combine to turn the MOSFET switches on at inappropriate times. Catastrophic circuit failure may then result.